The author recently obtained a number of mineral
specimens from the Phalaborwa Mine and since then has have been fascinated by
the beauty, variety and complexity of the minerals from this locality. During
the 1980’s, John Gliddon, a geologist at Phalaborwa mine amassed a large
collection of zeolites, sulphides and a host of rare minerals from the open
pit. However, after he left the mine, mineral specimens coming out this
locality virtually ceased. Gliddon reports in the Mineralogical Record (5.)
“attractive specimens of
zeolites and related minerals have been found lining some of the cavities in
dykes cutting across the Phalaborwa open pit. These must be some of the most
attractive zeolitic specimens yet reported from Africa, a continent not noted
for their occurrence”

Figure 1: The open pit mine at Phalaborwa as it is today (April 2004). Mining in the
open pit ceased a few years back and in 2000 shaft mining started. The dolerite dykes can just
be seen as dark grey intrusions crisscrossing the deposit.

The formation of
the Phalaborwa Complex is as fascinating as its mineral assemblage. Geologists
tell us that around 2 billion years ago a carbonate rich magma intruded the
granitic country rock welling up along fissures. The intrusion created a
pipe-like complex largely concentrically arranged consisting of mainly
pyroxenite, syenite and carbonatite. The intrusion occurred in several stages,
with the pyroxenite interacting with the country rock forming a felsphathic
pyroxenite along the area of contact between the two different rock masses (3)
It seems that several plugs of syenite was also injected into the granite. This
was followed by the formation of a course-grained pegmatoid emplaced in the
pyroxenite. Additionally, a breccia-like rock, called phoscorite and banded
carbonatite were emplaced within the central pegmatoid (3) Copper mineralization took place later
via ascending fluids (1.) The Phalaborwa Complex is unique in that it is the only economically
viable carbonatite-hosted copper deposit in the world(4)
Inclusions studied in apatite from phoscorite and
pyroxene found in the pyroxenite of the southern core of the Palaborwa Complex
bear portlandite, sulfates, and fluorite,
whose action as fluxing components explains the origin of the low-temperature
carbonatite magmas, even at moderate contents of alkalis (2.) There
is a network of dolerite dykes crosscutting the intrusive rocks of the Complex.
The important role of water is
highlighted by the occurrence of zeolites in the crystalline inclusions found
in the dolerite dykes (2.) The age of the dykes is of Waterberg age
(1.6 billion years) and varies in width and depth from a few centimeters to 50
meters (5.)

More than 50 different
minerals have been reported from the Palaborwa Mine (excluding trace minerals) (1.)
A variety of minerals are found within the intrusive rocks and the dolerite
dykes hosting secondary minerals such as zeolites. A range of secondary
minerals found in the dykes includes, analcime, biotite, calcite, chabazite,
datolite, flourapophyllite, heulandite, lamontite, mesolite, natrolite,
pectolite, prehnite, pyrite, saponite, scolecite, stilbite and thomsonite(5)
A number of rare and exotic minerals have been found in the complex and a few
of these include, iowaite, zirkelite, baddeleyite, chondrodite,
antigorite and valleriite.

Below are featured
several mineral specimens from the authors collection. These are meant to be an
introduction to some of the minerals and by no means a complete representation
or study of the minerals of the Phalaborwa Complex. Perhaps the sharing of this
information will be a catalyst in renewed interest in this locality.

Figure 2: A flat calcite and chondrodite matrix is amply covered with rich red chondrodite
crystals to 4mm across. A secondary dusting of minute magnetite and antigorite
covers the later crystallisation of the chondrodite making it appear black.
Field of view: 2x2cm

Figure 3: A single partially twinned section of magnetite crystal. There is minor calcite,
attached with chondrodite and deep turquoise coloured iowaite. The magnetite is
reported to be the largest ever (according to the original John Gliddon specimen label) collected at
Phalabora. Specimen size: 3x4cm

Figure 4: Good crystallisation of magnetite with associated calcite, ‘gemmy’ green clinochlore
and orange chondrodite. Also present are tiny secondary magnetite crystals and
a few minute purple fluorites. The largest exposed chondrodite is 8mm, the
orange colour is very unusual for the locality. Field of view: 2x2cm

Figure 7: A piece of massive baddeleyite with calcite that has several baddeleyite crystals
grown through. An excellent terminated 1cm crystal is exposed on one side of
the matrix. Specimen size: 6x4cm